Emerging standardization efforts, as in the IEEE organization, allow really considering strict resource reservation implementation at OSI level 2 (Link Layer). However, all these new mechanisms are not time correlated and thus do not allow to indicate the end-time of a current reservation or to schedule a future reservation.
In the present document the term “resource” relates to all network variables, such as bandwidth, jitter and latency, for instance, which characterize a data flow (or stream) between two nodes through a given infrastructure.
Some environments, such as professional video production and broadcast environments, are very time sensitive environment. So, it has been proposed to replace the point-to-point infrastructure they currently used with a packet switched network. But, this imposes to take care of about all latencies which could impact the overall system performances.
The well known OSI model (schematically illustrated in FIG. 1 and standardized by the ISO organization) defines a networking framework for implementing communication means in seven layers. Layers 1 to 4 are in charge of the transport of the data over a given communication medium, while layers 5 to 7 are used to allow different applications to communicate independently of the communication infrastructure used.
The present invention only concerns the OSI layer 2, i.e. the data link layer. So, all mechanisms described hereafter are handled at the OSI layer 2.
As it is known by the man skilled in the art, core network switches are core network equipments that forward traffic on information contained in the layer-2 header. This “forwarding” differs from “routing” which concerns operations on layer-3 information.
These core network switches only forward traffic to the addressees by using a forwarding table that associates a hardware address to one of their ports. When a frame is received by a core network switch, its layer-2 header gives the hardware address and thus an associated entry in the forwarding table, which designates the port to which the core network switch must forward the frame. Because they operate at a low level, network switches' processes are implemented in hardware, allowing mastering their latencies.
The IEEE 802.1 Audio/Video Bridging (AVB) Task Group (TG), which is part of IEEE 802.1, aims at providing specifications that will allow time-synchronized low latency streaming services through 802 networks. This TG comprises a sub-group “IEEE 802.1AS: Timing and Synchronization” which aims at defining through a standard Layer 2 time synchronizing service that is appropriate for the most stringent requirements of consumer electronics applications.
The 802.1AS standard specifies the protocol and procedures that must be used to ensure that the synchronization requirements are met for time sensitive applications, such as audio and video, across Bridged and Virtual Bridged Local Area Networks consisting of LAN media where the transmission delays are fixed and symmetrical, such as IEEE 802.3 full duplex links, for instance. This includes the maintenance of synchronized time during normal operation and following addition, removal or failure of network components and network reconfiguration. This 802.1AS standard specifies the use of IEEE 1588 specifications where applicable in the context of IEEE 802.1D and 802.1Q standards. Synchronization to an externally provided timing signal (e.g. a recognized timing standard such as UTC or TAI) is not part of this standard but is not precluded.
IEEE 802.1AVB task group comprises two other sub groups 802.1Qat and 802.1Qav concerning new resource reservation mechanism.
The 802.1Qat standard aims at defining an admission control system that allows bridges to guarantee the resources needed for Audio/Video (AV) streams. It specifies protocols, procedures and managed objects, usable by existing higher layer mechanisms, which allow network resources to be reserved for specific traffic streams traversing a bridged local area network. It identifies traffic streams to a level sufficient for switches to determine the required resources and provides a mechanism for dynamic maintenance of those resources.
This standard provides a signaling protocol to enable the end-to-end management of resource reservation for QoS guaranteed streams. The signaling protocol facilitates the registration, deregistration, and retention of resource reservation information in relevant network elements. The signaling protocol is an essential component for automatic configuration in bridged local area network applications that require latency and bandwidth guarantees. The application of current IEEE 802 technologies for high quality time sensitive streaming allows users to increase the load of their networks unknowingly to the extent that the user experience is negatively impacted. To provide the robust guaranteed QoS capability for streaming applications, the availability of network resources along the entire data path must be insured before transmission takes place. This requires the definition of traffic stream descriptors and a protocol to signal the resource reservation along the end-to-end path of streams. Multiple registration protocol (MRP) is used as a basis for this protocol.
The 802.1Qav standard aims at enhancing standard 802.1 bridge frame forwarding rules to support AV streams. It allows switches to provide guarantees for time-sensitive (i.e. bounded latency and delivery variation), loss-sensitive real-time audio video data transmission (AV traffic). It specifies per priority ingress metering, priority regeneration and timing-aware queue draining algorithms. Virtual Local Area Network (VLAN) tag encoded priority values are allocated, in aggregate, to segregate frames among controlled and non-controlled queues, allowing simultaneous support for both AV traffic and other bridged traffic over and between wired and wireless Local Area Networks (WLANs). This standard specifies enhancements to forward function of the above mentioned network switches (which are increasingly used to interconnect devices that support audio and video streaming applications) to provide performance guarantees allowing time-sensitive traffic in a local area network and harmonize delay, jitter and packet loss for Layer-2 networks.
The above mentioned new ongoing standardization efforts allow accurate synchronization connected network elements (end-node and core network equipment) and ensuring a strict resource reservation. Nevertheless, even if they aim at supporting time sensitive applications, they are not fully related because the resource reservation can not be scheduled according to the “wall” clock shared by any synchronized equipment.